@Michoel Are you asking "Were Avraham and Sarah required to convert others?" or "Were the people whom Avraham and Sarah converted obligated to do so?"?
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b aDec 30 '12 at 3:20

1

The later. The OP asked if any religions were required to convert with the advent of Judaism, not who did.
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MichoelDec 30 '12 at 3:29

4

Sorry to disagree, but they were not converted to Judaism, but rather to monotheism. As evidenced by the fact that they were not at Matan Torah.
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ArielDec 30 '12 at 5:46

@Ariel That was the "Judaism" of the time (even the Avos weren't at the giving of the Torah!). My intention in the answer is not changed by them not being technically Jewish, nor is it deviating from what I think the questioner meant.
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b aDec 30 '12 at 5:55

No such "switch" happened. According to the simplest understanding of Jewish history, Judaism started with one man, Avraham, who recognized the creator of the world. He came to this realization himself, independent of anyone else. G-d blessed him that his descendants would be numerous, and they were. Several hundred years later, his descendants stood at Mount Sinai and received the Torah from G-d.

Every Jew today is either a descendant of those people, descended from people who converted somewhere along the way, or are converts themselves. Judaism does not claim to "inherit" from any other religion as I understand Christianity and Islam claim to.